This invention relates to methods devices used for feeding hoses into boreholes as part of a mining operation. More particularly, the present invention relates to a method and apparatus for feeding a hose, such as a hose that is used for charging mining boreholes with liquid explosive, into generally upwardly oriented boreholes.
The success of underground mineral mining operations depends on efficient procedures for fracturing rock and extracting ore. One form of fracturing operation is known as sublevel caving and involves fracturing overhead rock formations in a controlled manner. A complete and continuous fracturing process is important to maximize ore recovery and avoid the high risk of unexpected collapse of overhead rock structure into the sublevel cave area.
The required systematic fracturing of rock structure is accomplished in part by drilling a set of substantially upright, overhead boreholes which are loaded with explosive material. These boreholes have diameters ranging from about 5.4 cm to about 11.4 cm and may be drilled in a fan pattern, in a ring pattern, in parallel orientation, or combinations thereof, depending on the desired pattern of collapse of superior rock structure.
Boreholes drilled in a ring pattern are not drilled equal distances from each other, primarily because of the configuration of the drill itself. A drill is set up at a fixed position in the working stope with the drill arm allowed to rotate to drill a ring. A typical ring is comprised of a set of boreholes drilled at angles up to 20 degrees about the axis of the drill arm. These blastholes are drilled in a fan-shaped pattern with as little as about 15 cm distance separating them at the drill bit entry points. Holes up to about 30 m long can be drilled with a typical separation at the toe of the hole of about 3.5 m.
When the ring of boreholes is loaded with explosives, typically by pumping a liquid explosive into upwardly oriented boreholes, there is a concentration of explosive material in the collar region due to the short distance between each hole in the ring because of the fan pattern. It would be desirable to have from about 4.5 to 14 m of non-loaded borehole, or collar, to avoid excessively high powder factors in the collar region. High powder factors tend to damage adjacent rings and can contribute to poor explosive loading conditions due to excessive cracking of the rock structure into other drilled holes.
Thus, it would be desirable to selectively adjust the collar in upwardly oriented boreholes loaded with liquid explosive. This selectivity would facilitate obtaining the proper collar required for specific rock conditions encountered in a particular mining operation. Advantages of this selectivity would include cost savings because of less liquid explosive used, increased safety by lowering the powder factor in the collar region of drilled holes, better rock fragmentation by avoiding the cratering action produced when borehole collars are loaded with explosive or "collar primed," and preventing cratering action into adjacent rings and thus permitting improved conditions for subsequent blasting operations.
U.S. Pat. No. 4,813,358 to Roberts describes an inflatable wand designed to be positioned within an upwardly oriented borehole. The wand includes a flexible tube for positioning along an elbow or bend in a borehole, a conduit through which liquid explosive may be pumped into the bore hole, and capacity to be inflated to radially expand and seal the opening of the borehole so that the liquid explosive is retained within the borehole. If the inflatable wand could be threaded an appropriate distance up a borehole, the problem of providing adjustable collars would be solved. It is extremely difficult to manually push the wand up into a borehole more than about 1.5 m because the wand becomes very slippery when coated with liquid explosive and is heavy due to the combined weight of the wand and liquid explosive.